The present invention is for a method for producing a high surface area iron material, comprising predominantly amorphous or poorly crystalline iron oxides, starting with a low surface area iron metal. The iron material of the present invention has a surface area of at least about 200 m2/g, and is prepared via a method which comprises reacting a low surface area iron metal with oxygen and an organic acid. The high surface area iron material formed via this method is essentially free of contaminants.
Iron-based catalysts are known in the art for use in a variety of chemical reactions. For example, in water gas shift reactions it is common practice to employ chromium-promoted iron catalysts in a high temperature first stage (referred to as a high temperature shift or HTS reaction) to effect carbon monoxide conversion at temperatures above about 350° C. and to reduce the CO content to about 3%-4% (see, for example, D. S. Newsom, Catal. Rev., 21, p. 275 (1980)). A typical composition of high temperature shift (HTS) catalyst comprises from about 60 wt % to about 95 wt % Fe2O3, from about 0 wt % to about 20 wt % Cr2O3, from about 0 wt % to about 10 wt % of CuO and from about 0 wt % to about 10 wt % other active components such as ZrO2, TiO2, Co3O4, Al2O3, SiO2 and/or CeO2.
Since the 1950's iron-based Fischer-Tropsch catalysts have been successfully used in fixed-bed, fluidized-bed and slurry phase reactors, and there have been several methods used for the preparation of iron-based Fischer-Tropsch catalysts. The earliest catalysts, prepared by Fischer, were iron turnings treated with alkali. At high pressure, the liquid product was rich in oxygenated compounds, and at lower pressures hydrocarbons were produced. However, the iron-based catalysts prepared by this method deactivated rapidly.
Various types of iron precursors are known for use in the production of catalysts. For example, iron-based Fischer-Tropsch catalysts often have a catalyst precursor usually composed of high surface area corundum phase iron oxide (α-Fe2O3 or hematite). Microcrystalline phases of iron oxides such as ferrihydrite, goethite and lepidocrocite, distinct minerals in the family of oxides, hydroxides and oxyhydroxides of iron, are common precursors to some of these other iron oxides such as hematite and magnetite, and hence, have value as starting materials for catalyst production. Further, ferrihydrite has been used directly as an absorbent and a catalyst. Because of its utility as a high surface area precursor for iron-based catalysts, it would be advantageous to have a process for preparing ferrihydrite that does not require numerous washing steps, but that resulted in a ferrihydrite contained few to no contaminants when prepared.